Some display devices such as liquid crystal television receivers are equipped with a flat speaker. The flat speaker disclosed in PTL 1 includes a diaphragm having a flat plate shape, an exciter that is attached on a back surface of the diaphragm, and a fixing member that fixes an outer circumference of the diaphragm in a circumferential direction. The diaphragm configures a display panel of a display device. A vibration of the exciter is transmitted to the diaphragm, and sound is emitted from the diaphragm.